There has conventionally been devised a one-motor hybrid drive device in which an output shaft (member) of an internal combustion engine is coupled to an input shaft (member) of an automatic transmission device via a K0 clutch and in which a rotor of an electric motor is coupled to the automatic transmission device. In general, the hybrid drive device starts the vehicle using the drive force of the electric motor, engages the K0 clutch when the vehicle is at a predetermined low speed to start the engine, and drives the vehicle using the drive force of the engine while performing shifting in the automatic transmission device. In this event, the electric motor outputs power so as to assist the drive force of the engine, generates electric power using the drive force of the engine or the inertial force of the vehicle, or idles.
In the case where the charge amount (SOC) of a battery is insufficient, the vehicle is started using power of the internal combustion engine. In this event, the K0 clutch functions as a starting clutch. When the engine is started by the electric motor and when the vehicle is started by the engine, the K0 clutch is subjected to slip control in order for a shock due to abrupt torque fluctuations between the input side and the output side of the K0 clutch to be avoided.
In the hybrid drive device, the electric motor is a large-diameter hollow motor, and the K0 clutch is disposed in the radially inner portion of the rotor of the motor to achieve downsizing and improve the efficiency of the electric motor. Lubricating oil is supplied from the input shaft of the automatic transmission device to the K0 clutch. After lubricating and cooling the K0 clutch, the lubricating oil flows toward a coil end of the electric motor (see Patent Document 1).
In some hybrid drive devices, the clutch is lubricated by a full-dip method. That is, the K0 clutch is housed in a liquid-tight unit housing, the housing is filled with lubricating oil, and the lubricating oil in the housing is circulated through a lubricating oil passage that passes by way of an oil cooler (see Patent Document 2).